Adjustable magnetic snap-action pressure switch



June 8, 1965 ADJUSTABLE MAGNETIC SNAP-ACTION PRESSURE SWITCH Filed July 1962 l4 I i 28- FIG. 2

W. D. HUSTON III 2 Sheets-Sheet 1 IN V EN TOR.

WILLIAM D. HUSTON BY ATTORNEY 5 ADJUSTABLE MAGNETIC SNAP-ACTION PRESSURE SWITCH Filed July 5, 1962 W. D. HUSTON June 8, 1965 2 Sheets-Sheet 2 4 i El 8 7 B% Q (A w L n| A MW 6 5 %4 w w 9 4/ x fi m E Hhflu & \H 2 3% 7 7 6 6 B Q MN 6 5 6 FIG. 5

INVENTOR.

WiLIAM D. HUSTON United States Patent C) 3,188,420 ADJUSTABLE MAGNETEC SNAP-ACTXQN PRESSURE SWITtlH William D. Huston, Rochester, N.Y., assigncr to American Radiator 8: Standard danitary Corporation, New York,

N.Y., a corporation of Delaware Filed July 5, 1962, Ser. No. M37562 14 (Ilaims. (Qt. 290-315) This invention relates to a hermetically sealed pressure-operated electrical switch, ,and more particularly to an electrical switch operated by fluid pressure.

A true snap-acting switch wouldappear to have an important place in aircraft circuits where there is high vibration and shock. However, anything less than a positive snap from o to onT and vice versa would permit erratic action and what is called teasing. Teasing is when the switch fails to snap clean from an on or cflf position, and maintains a momentary or high resistance contact before making a clean break to the opposite position. This teasing action occurs principally in mechanical switches where there is backlash, friction, and shifting of the parts, which prevent a clean snapbreak of the switching elements. For these reasons, attempts have been made to adapt pressure-actuated switches to aircraft use.

ressure switches have been subject to many deficiencies in the past. There have been problems due to friction in the operating mechanism which can change the switch setting and the calibration of the switching point. There have been particularly severe problems arising from chatter and frying of the contact points when the switch is subjected to shock and vibration conditions in use.

Furthermore, difiiculties'have been encountered in sealing the switches so as to prevent dust and dirt collecting in and around the contacts, and to obviate corrosion of the contacts. To avoid corrosion, flash gold plating is often used, but this-is not permanent insurance if the switch housing is not fully sealed. In aircraft service the switch must also be sealed to avoid corona eifects at high altitudes.

Further, prior types of pressures switches have commonly been used at nominally low temperatures and have not been adapted for use at temperatures above 250 F. Moreover, while prior types of pressure switches have been nominally sealed from changes in internal pressure, they have not been sealed to prevent change in pressure calibration or change in electrical characteristics with changes in altitude. In order to function properly in an airplane or in a missile, however, it is essential that pressure switches withstand extreme temperatures, speeds, and pressures. It is desirable furthermore for such uses that pressure switches be small in size and highly reliable even under the adverse conditions of pressure, temperature, vibration, and shock under which they have to operate.

Conventional pressure switches are made with 2. diaphragm pressure sensing element or a C spring Bourdon tube element. The pressure-measuring element in either form is normally connected to a set of switching blades which are actuated at a predetermined pressure. Alternately, however, a snap action mechanism is con- I nected to the pressure-measuring element to give snap aisasze ice Another object of the invention is to provide a pressure switch of high reliability and capable of excellent performance, but of small diameter and reasonable length.

A further object of the invention is to provide a pressure switch which will be highly reliable in operation, and in which the unit is so assembled and housed that chances of collection of dust and dirt on the contacts is minimized and corrosion of the contacts is prevented.

Another object of the invention is to provide a selfcontained pressure switch which will operate at extreme temperatures and under adverse environmental conditions.

Still another object of the invention is to provide a pressure switch of simple, highly rugged design.

Another object of this invention is to provide an improved pressure-operated switch which'is reliable at temperatures above 250 Fahrenheit, and which is hermetically sealed to prevent changes in the pressure cali- 'bration or the electrical characteristics of this switch.

It is a further object of this invention to provide an improved pressure switch from which teasing and chatter are eliminated and which will provide reliable action even over an extended period of use.

A still further object of this invention is to provide an improved pressure switch which employs a minimum of moving parts, andvwhich is dynamically and statically balanced so as to render it highly resistant to shock and vibration.

An additional object of this invention is to provide an improved pressure switch which is adjustable so that its electrical switch may be set to open at a selected predetermined pressure.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a plan view illustrating a hermetically sealed fluid pressure switch made in accordance with one embodiment of this invention;

FIG. 2 is a view taken along the line 2-2 of FIG. 1 and looking in the direction of the arrows;

FIG. 3 is a sectional view taken along the line 3 -3 of FIG. 2 and looking in the direction of the arrows;

FIG. 4 is a plan view of a further embodiment of this invention;

FIG. 5 is a section taken along the line 55 of FIG. 4 and looking in the direction of the arrows; and

FIG. 6 is a sectional view taken along the line 6-6 of FIG. 5 and looking in the direction of the arrows.

The pressure switch of the present invention is enclosed in a hermetically sealed housing that is completely gas tight. This permits pressurizing the housing to improve the electrical characteristics and prevent change in pressure, which might deteriorate the electrical switching characteristics at low ambient pressures. The switch is designed with a basic minimum of moving parts, comprising simply a pressure measuring element, preferably a helical Bourdon tube, a magnet and armature, and a single set of switch points to make and break the electrical contact. By reducing the number of mechanical parts in the switch, resistance to shock and vibration, and accuracy are improved. The magnet retains the armature in one position.

The switch of the invention differs from the conventional snap-acting switch in that a permanent magnet operating with a movable armature replaces the over-center spring normaliy associated with a snap-acting switch. The magnet-armature combination of the present invention locks the pressure measuring element, the Bourdon tube, in position until the spring force on the armature from the pressure measuring element overcomes the magnetic pull between the armature and the magnet,

'1.) and snaps the armature to the second position where it is again locked by the magnet. By opposing the magnet force against the armature with the spring force of the pressure measuring element, the armature and the electrical contacts operated'by the armature are locked in two positions, off and on, until switched by change in the pressure applied to the pressure-measuring element.

In the switches illustrated, a helical Bourdon tube is used as the pressure-measuring element; It iscentered on a pivotor'fulcrum at the center of the helix. The armature is rigidly connected to the free end of the helical coil and in practice serves as the bearing or fulcrum point for the center of the helix. This provides a fully balanced mechanical arrangement which is not subject to vibration or shock in use. Since the helical Bourdon tube is a rotating device, if the rotation is centered on a single pivot or fulcrum, there will be no unbalanced elements in the system which can be disturbed by vibration or shock loads.

In the specific embodiments of the invention illustrated, the armature is mounted to swing between opposed end faces of the permanent magnet which are spaced further apart than the thickness of the armature. Hence, when one side of the armature is held against a first end face of the magnet, the opposite side of the armature is spaced several degrees away from the second end face of the magnet. When the force in the helical coil overcomes the magnetic force on the first face of the armature, the armature will snap the second face of the armature against the second face of the magnet. The character of the snapaction can be controlled by changing the spring characteristics of the Bourdon coil. can be adjusted to be sustained through more or less angular travel. To increase the absolute force in the snap action of the armature, themagnet force can be increased, and the force of the pressure-measuring element (Bourdon'tube) can be increased. A variation is to maintain a given absolute force in the magnet and in the pressure-measuring element but to vary the rate of build-up of the force. in the pressure rneasuring element. With a rapid build-up of force'in the pressure-measuring element or a highs'pring rate, thesnap action will be heavy but will carry over a. short distance only. With a slow build-up of force in the pressure-measuring ele- V sealed terminals. The contacts are supported by a mounting plate which is carried against a metal gasket seal at the top of the switch. This is used to provide adjustment of the switching point. After adjustment, the mounting plate is locked in place by a large hollow nut' that surrounds the electrical terminals at the top of the switch.

' Referring now to the drawings by numerals of reference, and first to the embodiment of the invention shown in FIGS. 1 to 3 inclusive, ll'designates generally a stainless steel housing which is externally threaded as at 12 so that the pressure switch maybe mounted securely in place. The housing 11 is formed with a flange 13 above which there is a hexagonally shaped portion 14 to which a wrench may be applied to screw the housinginto place. The housing is closed at its lower end except for an opening in which the open end 15 of a helical Bourdon tube 16 is secured by silver solder or the like.

The housing is open at its upper end and is internally threaded to receive a ring-nut 19 of stainless steel, which is externally shaped to permit the adjustment thereof by a wrench. Interposed between nut 19 and an annular shoulder or ledge 20 on the interior of housing 11 is a stainless ,steeladjustment plate 22 which has an integral This spring force annular flange 23 disposed beneath nut 19 and on top of an internal sealing C-ring 24 which rests upon the ledge or shoulder 20. V

' Inserted snugly within the smooth interior of nut 19 is an insulating cap 25 of glass, bonded mica or the like, the top of which is hollowed out to form a depression 26 therein. Cap 25 is fixed to plate 22 by screws 27 which thread into bosses 28 on the upper surface of the plate 22.

Fixed in the depression 26 in cap 25 are threaded, preferably nickel alloy terminals 29, the heads of which are at their lower ends and are denoted at 30. The terminals are secured in place by nuts 32, and carry washers 33 and nuts 34 by which wire leads may be secured to the terminals. As previously noted, cap 25 should be manufactured from a dielectric material so that neither the terminals nor the electrically conductive elements thereon will be grounded or shorted against nut 19.

Fixed to and extending through the stainless steel adjustment plate 22 are spaced, tubular insulators 35, 35 in which are fixed electrically conductive pins or studs 37, 37 which are connected at their upper ends, between plate 22 and cap 25, to the heads of terminals 29, by means of leaf-spring type conductors 36. The pins or studs 37, 37' depend from the lower ends of the insulators and 35' and upon stud 37 there is fixed one end of the metallic, leaf-spring switch blade 39. The opposite end 40 of the switch blade 39 is free. In FIG. 3, switch blade 39 is shown with its free end out of engagement with the stud 37". Thus positioned, the switch is open.

' Switch blade 39 is actuated by an armature assembly which is directly responsive to the tubular pressure spring or Bourdon tube 16. As shown in FIG. 2, a block 42is threaded into the upper or closed end of the tube 16.

This block is preferably made of dielectric material and is secured to the Bourdon tube so as to rotate or oscillate upon increase or decrease of pressure in the tube. Fixed in the upper endof block 42 is a centering pin 44, whose opposite end is rotatably mounted in adjustment plate 22. Pin 44 thus serves to center block 42 in coil 16, at the same time permittingblock 42 to oscillate with pressure coil 16 as the latter expands and contracts with changes in the pressure of the fluid being measured.

The block 42 has an upper end portion 45 of reduced diameter; and fixed on this portion 45 is a soft magnet steel armature 46, which has oppositely outwardly projecting ends 47 and 48. Extending laterally from end 48 of armature 46 is a pin 48 which, upon clockwise movement of the armature in FIG. 3, serves to disengage free end 40 of switch blade 39 from its cooperating'st-ud 37'.

To prevent chatter between switch contacts 40 and, 37', an arcuate-shaped permanent magnet-49 is suspended by posts 50 from adjustment plate 22 to partially surround the portion 45 of block 42, and to be in operative relation to armature 46. The magnets pole faces 51 and 51 are rectangular in cross section, a

Switch blade 39 is designed to be'closed at low pressure. To adjust the switch so that it will be opened at a predetermined pressure, nut 19 is loosened, andcap 2 5'and hence adjustment plate 22, and magnet 49 are rotated slightly to a selected position, and nut 19 is then ret'ightened..

Turning to FIG. 3, it should be understood that increase in pressure will cause Bourdon tube 16 to expand and turn armature 46 in a clockwise direction so that pin 48 on armature arm 48 will open switch 39 as illustrated in FIG. 3. Before being subjected to pressure, end 48 of the armature would be securely held against pole face 51'. As

51, causing an instantaneous and clean break between switch contact 4%) and the cooperating lug 37. This switching phenomenon is very similar to a snap "faulty operation when exposed to vibration or shock,

while the magnetic-armature combination is far more stable when subjected to similar conditions, because of thepole. faces which hold the switch armature securely in either its switch opening or closing position. Unlike the over-center spring switch, the magnetic switch, moreover provides a snapping force which is not subject to fatigue, heat, or pressure failures, and which avoids the teasing phenomenon during switching.

, To increasethe selected pressure at whic'n switch 39 will be opened, the pressure switch is adjusted by loosening nut19 and turning cup 25 and hence pins 37, 3'7 and magnet 49 slightly clockwise from the positions shown in FIG. 3, thus increasing the amount of pressure which must .be built up in tube 16 before it expands sufliciently to cause armature 46 to rotate away from pole face 51' to the position shown inFIG. 3. Conversely, switch 39 will be opened at a lower pressure if magnet 49 is rotated slightly counterclockwise from the position shownin FIG. 3.

The pressure switch made according to this first em bodiment of the invention is hermetically sealed in housing 11 by the silversolder or braze around tube end and by C-ring 24. The housing may, therefore, be" pressurized by filling it withan inert gas under pres sure, thereby to improve switch efliciency. By maintain ing the interior of the housing 11 under constant pressure, pressure changes. are avoided which would deteriorate the electrical switching characteristics of switch 39. Also,

since armature block 42 and centering pin 44 prevent lateral movement of the closed end of the pressure coil 16, while at the same time serving to position the coil concentrically with respectto the fixed end 15, there will be no unbalanced elements in the system which can be excited by vibration or shock loads.

, In FIGS. 4 to 6 a further embodiment of this invention isillustrated. 61 denotes a bell-shaped housing which is closed at one end 62 and has a portion 63 of its peripheral surface threaded intermediate its ends to permit the housing to be screwed into place. Housing 61 ,at its upper or open end has a hexagonal peripheral portion 64' whereby it may be threaded into place; and below this hexagonal portion is a circumferential flange 65. Mounted in the housing 61 is a helical Bourdon tube 66 with its open end 67 fixed by, silver brazing com- "pound, or the like, in .an aperture in the lower end wall of the housing. p For positioning the upper end of the pressure switch unit, the housing is internally threaded at its upper end to receive an annular stainless steel nut 72. The nut 72 has four notches 72 in its inner face to receive a key wrench orjthe like for threading the; nut into and out of the housing 61. interposed between nut 72 and an annular ledgeor shoulder 73 on the interior of the housing 61 is 'a disc-shaped, dielectric adjustment plate 74, which has an annular flange portion 75 extending laterally outwardly over the top of an internal seal "or C-ring 70 which rests upon the ledge 73. When the nut 72 is screwed snugly into housing 61, it cooperates with the C-ring 70 to lock the adjustment plate 74 in an adjusted angular position in the housing.

Screwed into the bottom of adjustment plate 74 centrally thereof, is a dielectric positioning or centering pin 76 which extends downwardly along the axial center line i of housing 61 and through the axial bore 77 of a block 78 that is threaded into the upper end of the Bourdon tube 66. The block has a helical flange 79 which engages between convolutions of the tube 66, whereby upon expansion or contraction of tube 66, block 78 will rotate about centering pin 76. Mounted on pin 76 above block 78 for rotation on the pin is an elongate armature or switch blade 84 of soft magnetic steel. The block 78 has diametrally opposed arcuate portions 83, on its upper end which are positioned to engage blade 84 to move the blade upon rotation of the block in one direction or the other. Positioned slightly above the upper face of switch blade 84 and integral with centering pin 76 is an annular flange 85 which limits the axially upward movement of blade 84. (See FIG. 5.)

Rotatably disposed on centering pin 76 intermediate flange 85 and the bottom of adjustment plate 74, are two axially spaced switch hanger plates 86 and 87. One plate 86 is flush with the bottom of adjusting plate 74; and the other plate 87 rests upon the upper surface of flange 85. Rotata'oly positioned on centering pin 76 between the plates 86 and 87 is a permanent ceramic magnet 88 of the type which is electrically non-conductive. Switch hanger plates 86 and 37 are shaped essentially in the form of annular rings with outside diameters equal to that of permanent magnet 58; each blade, however, has a lug thereon which extends radially outwardly. As shown in FIG. 5, plates 86 and 87 are positioned about centering pin 76 in such manner that their respective logs are essentially diametrically opposite one another and have projecting axially therefrom, and integral therewith, a pair of spaced legs or switch contact elements 86, 86 and 87', 87". These plates and switch elements are-not only electrically conductive but are made of paramagnetic material. The legs or switch elements straddle opposite ends of switch blade 84, thus defining at both ends of blade 84 two pole faces of one horseshoe shaped magnet. These pole faces restrict the oscillatory motion of switch blade 84 about the axis of the Bourdon tube.

In addition to being pivotally mounted in axially spaced relation on the centering pin 76, the switch hanger plates 86 and 87 are rigidly secured to adjustment plate 7 4 where by rotational adjustment of the latter about the axis of housing 61 will cause a corresponding rotational adjustment of switch hanger plates 86 and 87 and the respective legs or switch elements depending therefrom. The switch hanger plate assembly 86 is secured to adjustment plate 74 by a screw 89 which passes upwardly through the lug on plate 86 between legs 86' and 86" thereof, and

"through adjustment plate '74 where its upper end is se- 87 and adjustment plate 74, and through the latter; and

its upper end'is secured by a nut 94 to plate 74.

Secured to and extending from the outer face of adjustment plate 74 are two conventional electrical terminals (similar to 29 in FIGS. 1 to 3) designated generally at 95'and 96. Respective terminals 95 and 96 are connected by electrically conductive jumper straps 9 7 and 98 and nuts 94 and 90, respectively, to screws 92 and 89, respectively.

The armature or switch blade 84 has the ends thereof on two diagonally opposite surfaces of the blades (facing poles 86 and 87") coated with a dielectric material as at 1% and 161 to provide means for opening the switch circuit; but the two remaining diagonal end surfaces (facing 86" and 87') are free of insulation, hence electrically conductive. As in the case of the embodiment shown inFlGS. 1 to 3, the pressure switch is designed to provide a closed circuit at low pressure (i.e., atall pressures below a predetermined fluid pressure), at which point the conducting surfaces of blade 84 will engage switch elements 86" and 87 as shown in FIG. 6.

At a predetermined increased pressure, pressure tube 66 will expand so that its slotted neck portion turns clocka ssgao 7 tive forces which poles 86" and 87 exert on opposite ends of the blade. However, in much the same manner as described above for the embodiment shown in FIGS. 1 to 3., as 84 continues to be forced clockwise by the pressure coil, it reaches a point where the blade ends are suddenly attracted by other poles 86 and 87" thus causing 84 to snap suddenly into its other, or open-circuit, position where dielectric surfaces 100 and 101 engage the pole faces or switch elements 86 and 87", respectively. When the fluid pressure falls below the predetermined switching pressure the switch functions in a similar but opposite direction to close the circuit.

As in the case of the first embodiment, the preselected switching pressure may be adjusted by backing oif nut 72, rotating adjustment blade 74 slightly in either direction, and then retightening the nut. With respect to FIG. 6, assuming plate 74 had been adjusted slightly clockwise, pole faces'86 and 87' would have been moved closer to respective ends of switch blade 84. A greater pressure and a corresponding greater expansion of pressure tube 66 would then be required to 'pivot switch 84 clockwise away from magnetic switching elements 86" and 87 and into contact with elements 86' and 87".

Since the only moving parts in the pressure switch illustrated in FIGS. 46 are designed to rotate or oscillate concentrically about the axially aligned center pin 76, the unity is essentially free of unbalanced elements which might be excited by vibration or shock loads. In addition, with the employment of four magnetic pole faces, a pair for each end of the switch plate, teasing is avoided and a stable and reliable snap action switch is provided; one which will eliminate the frying of electrical contacts'and the chatter therebetween which might normally result from vibration or shock loading. Again, as in the case of the embodiment of FIGS. 13, the interior of the housing is sealed against pressure leaks so that it may be pressurized to further stabilize the electrical switch characteristics;

In both of the foregoing embodiments, it should be noted that the spring characteristics of a magnetic snap-type switch of the type disclosed herein, may be altered as desired merely by installing magnets or pressure tubes of dilferent characteristics. For instance, the absolute force in'the snapv action of the switch blade or armature may be increased by employing magnets which exhibit stronger magnet fields. Further, to sustain the snap action through a' more or less angular degree of travel, one may employ a pressure measuring element which exhibits a rapid build up of force thus producing a strong or heavy snap action which will rapidly expire over a short distance; or, one may employ a slow build up type of pressure measuring element wherein the force (exerted against an armature which is being held against the face of a magnetic pole) will be sustained through a greater degree of angular travel of the switch blade;

There is a basic difference between the snap action of the switch of the present invention, and the snap action of a mechanical switch. The mechanical switch has a simple over-center action. 'The spring force against the levers is slowly increased to the point of instability where the blade snaps to its second position. In the magnetic switch of the present invention, the armature force slowly decreases until'the forces of the pressure spring (Bourdon tube) overcomes the magnet force and the switch snaps in position. The magnetic switch acts by balance of force between the magnet and the pressure spring, while the mechanical snap-action switch operates by over-center action.

While the invention has been described in connection with the use of a helical Bourdon tube as the pressure spring, it will be understood that a spiral Bourdon tube might be used instead. The helical Bourdon tube permits use of a housing of smaller diameter but elongate. The spiral Bourdon tube makes possible a shallower housing but requires one of larger diameter.

While the invention has been described in connection with a specific embodiment thereof, it will be understood that it is capable of further modification, and this application is intendedto cover any variations, uses, oradaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention per,- tains and as may be applied to the essential features hereinbefore set forth, and as fall withinthe scope of the invention or the limits of the appended claims. a

Having thus described my invention, what I claim is:

1. A condition-responsive device comprising (a) ahousing,

(b) an electrical switch positioned in said housing and operable to open and closed positions, respectively, I

(c) a condition-responsive means in said housing, said means being movable in opposite directions in response to predetermined changes in a condition existing at the exterior of said housing,

(d) a paramagnetic lever mounted intermediate the is open, and the other of said poles engages and op poses movement of said lever, when said switch is closed, and

(f) means for adjusting said poles in said housing to alter the value of the predetermined changes which effect movement of said condition-responsive means.

2. A condition-responsive device as defined in claim 1 wherein (a) said lever is pivoted intermediate its ends about a stationary axis, and

(b) said adjusting means includes a movable support plate for mounting said magnetic means with its two poles adjacent the opposite ends, respectively, of said lever, and i (c) said support plate is rotatably adjustable in said housing about the pivotal axis of said lever to shift said poles, angularly relative to the two ends of said lever.

3. A condition-responsive device as defined in claim 1 wherein (a) said switch includes two spaced conductors extending inwardly of said housing,

*(b) a switch blade is fixed at one of its ends to one of said conductors, and the opposite end of said blade is free and normally urged in a direction to engage the other of said conductors, when said lever is in engagement with said other pole, and I (c) said lever has a projection thereon which is movable therewith to disengage said free blade end from said other conductor and to open said switch when said lever is moved into engagement with said one pole.

4. A condition-responsive device as. defined in claim lwherein i (a) said switch includes two spaced electrical conductors, v

(b) each of said conductors extends inwardly of said housing and defines therein a free end comprising a pair of closely spaced legs,

(c) said lever is electrically conductive and extends between said conductors and has one of its ends positioned between one of said pairsof conductor legs, and the other of its ends positioned between the other of said pairs of conductor legs, and one face of said one lever end and the diagonally opposite face of said other lever end have dielectric material thereon.

5. A pressure switch comprisin ,(a) a housing. 7

(b) a Bourdon tube mounted in said housing and having its open end fixed in said housing for connection to a fluid pressure source,

*() a pair of electrical terminals,

(d) a switch member movable to connect and disconnect said terminals to close and open an electric circuit,

(e) a switch actuating member connected to said Bourdon tube adjacent the closed end of said Bourdon tube and operative to move said switch member in opposite directions upon expansion and contraction of said tube,

(f) magnetic means having at least two spaced poles positioned in operative relation to one of said members to resist movement of said one member in opposite directions, respectively, one of said poles resisting movement of said switch member from closed to open position, and the other of said poles resisting movement of said switch member from open to closed position, and

(-g) means mounting said magnetic means in said housing for adjustment of said poles relative to said Bourdon tube to determine the amount of pressure required in said tube to move said switch member to open said circuit.

6. A pressure switch as claimed in claim 5, wherein said switch member is v (a) a leaf spring secured at one end to one of said terminals and having its opposite end constantly urged into engagement with the other of said terminals to close said switch, and said switch actuating member is (b) a double-armed lever mounted on said Bourdon tube and movable in one direction to disengage said opposite end of said spring from said other terminal, and said mounting means comprises (c) a support plate positioned in said housing for mounting said one pole adjacent one end of said lever for engagement thereby upon movement of said lever in said one direction, and for mounting said other pole adjacent the opposite end of said lever for engagement thereby upon the movement of said lever in the opposite direction.

7. A pressure switch as claimed in claim 6, wherein (a) said Bourdon tube is a helical Bourdon tube,

(b) means is provided to hold the closed end of said Bourdon tube against lateral movement but permitting rotary movement thereof about the helical axis of said tube,

(c) said lever is secured to said Bourdon tube to rotate coaxially of said helical axis upon expansion and contraction of said tube, and

(d) said support plate is mounted in said housing for rotary adjustment about said helical axis to shift said poles relative to said lever to determine the pressure required to move said lever in either direction about said helical axis.

8. A pressure switch as claimed in claim 5, wherein (a) said Bourdon tube is a helical Bourdon tube,

'(b) said switch actuating member is provided to hold the closed end of said Bourdon tube against lateral movement in said housing but permitting rotary movement thereof about the helical axis of said tube upon the expansion and contraction of said tube,

(c) said switch member is a blade mounted intermediate its ends in a slot in the top of said switch actuating member for limited rotation relative thereto about said helical axis, and for rotation with said switch actuating member upon a predetermined expansion and contraction, respectively, of said tube,

(d) said two poles project into the path of rotation of It) said blade adjacent diagonally opposite ends there or", (c) said terminals project into the path of rotation of said blade adjacent the remaining diagonally opposite ends of said blade, and said mounting means comprises '(f) a plate r-otatably adjustable in said housing, and

. A pressure switch comprising (a) ahousing (b) a helically wound Bourdon tube in said housing having its open end fixed in said housing for connection to a fluid pressure source,

(0) a block fixed to the closed end of said Bourdon tube, ((1) means for oscillatably mounting said block in said housing to rotate coaxially of the helical axis of said tube upon expansion and contraction of said tube,

(e) electrical switch means positioned in said housing,

(f) a lever mounted intermediate its ends on said block and oscillatabie coaxially therewith from one position to another to respectively open and close said switch means, and

(g) magnetic means positioned adjacent each of the ends of said lever and tending to attract and hold a respective end with increasing force as the latter approaches said magnetic means, whereby the pressure switch tends to be balanced and less subject to failure resulting from vibrations or shock loads.

it). A pressure switch as defined in claim 9 wherein (a) said lever is electrically conductive and wherein (b) one side of each end thereof is coated with a dielectric material,

(c) said material is on diagonally opposite sides of said lever, and wherein said electrical switch means comprises (d) two spaced conductors fixed to and extending inwardly of said housing, each of said conductors including (o) a pair of spaced contact elements, and

(f) each end of said lever is interposed between a respective pair of said contact elements, whereby in one position of said lever said dielectric material is interposed between said lever and said spaced conductors to open said switch means, and whereby said lever serves to electrically interconnect said spaced conductors and close said switch means when in said another of its positions.

11. A switch comprising (a) a housing,

(b) a condition-responsive device mounted in said housing,

(0) a magnet secured in said housing and having a pair of spaced poles,

(d) an armature connected to said condition-responsive device to be movable in opposite directions upon operation of said device, said armature being made of para-magnetic material and having opposite ends thereof disposed in operative relation to said spaced poles of said magnet, whereby movement of said armature in one direction is resisted by one of said magnet poles, and in the opposite direction by the other of said poles,

(e) a pair of electrical contacts,

(f) means operated by said armature upon movement thereof in opposite directions for opening and closing an electrical circuit through said contacts, and

(g) means for adjusting said magnet relative to said housing and to said condition-responsive device thereby to determine the condition necessary for moving said armature in said opposite directions.

12. A hermetically-sealed fluid-pressure switch com prising (a) a housinghaving an aperture in one end,

(b) a plate positioned in and sealing off the other end of said housing,

(c) a helically wound Bourdon tube mounted in said housing to have its open end sealed in said aperture for connection to a source of fluid pressure,

(d) switch-operating means including (e) a lever made of paramagnetic material,

(f) means mounting said lever in said housing, for oscillatory motion about the helical axis of said Bourdon tube upon expansion and contraction of said tube, a

(g) electrical contacts mounted in said housing adjacent said lever and operable by the latter, respectively, to open and close an electrical circuit through said contacts, and

(h) spaced magnetic means mounted on said plate and extending into said housing'adjacent opposite ends of said lever to resist movement of said lever,

(i) said plate being adjustable angularly about the helical axis of said tube to determine the. pressure 25 said lever comprises (b) a centering pin mounted at one end in said block and at its opposite end in said plate to guide said block and lever for oscillation coaxially of said 15 helical axis.

References Cited by the Examiner UNITED STATES PATENTS 1,782,458 11/30 Brennen 200 153 2,204,792 6/40 Davis.

2,556,582 6/51 Hansen 200-138 3,004,431 10/61 Studenick 200-81 BERNARD A. GILHEANY, Primary Examiner.

nected to said lever, and said mounting means for, 

9. A PRESSURE SWITCH COMPRISING (A) A HOUSING (B) A HELICALLY WOUND BOURDON TUBE IN SAID HOUSING HAVING ITS OPEN END FIXED IN SAID HOUSING FOR CONNECTION TO A FLUID PRESSURE SOURCE, (C) A BLOCK FIXED TO THE CLOSED END OF SAID BOURDON TUBE, (D) MEANS FOR OSCILLATABLY MOUNTING SAID BLOCK IN SAID HOUSING TO ROTATE COAXIALLY OF THE HELICAL AXIS OF SAID TUBE UPON EXPANSION AND CONTRACTION OF SAID TUBE, (E) ELECTRICAL SWITCH MEANS POSITIONED IN SAID HOUSING, (F) A LEVER MOUNTED INTERMEDIATE ITS ENDS ON SAID BLOCK AND OSCILLATABLE COAXIALLY THEREWITH FROM ONE POSITION TO ANOTHER TO RESPECTIVELY OPEN AND CLOSE SAID SWITCH MEANS, AND (G) MAGNETIC MEANS POSITIONED ADJACENT EACH OF THE ENDS OF THE LEVER AND TENDING TO ATTRACT AND HOLD A RESPECTIVE END WITH INCREASING FORCE AS THE LATTER APPROACHES SAID MAGNETIC MEANS, WHEREBY THE PRESSURE SWITCH TENDS TO BE BALANCED AND LESS SUBJECT TO FAILURE RESULTING FROM VIBRATIONS OR SHOCK LOADS. 